From: Yu Kuai <yukuai3@xxxxxxxxxx> User will configure allowed iops limit in 1s, and calculate_io_allowed() will calculate allowed iops in the slice by: limit * HZ / throtl_slice However, if limit is quite low, the result can be 0, then allowed IO in the slice is 0, this will cause missing dispatch and control will be lower than limit. For example, set iops_limit to 5 with HD disk, and test will found that iops will be 3. This is usually not a big deal, because user will unlikely to configure such low iops limit, however, this is still a problem in the extreme scene. Fix the problem by making sure the wait time calculated by tg_within_iops_limit() should allow at least one IO to be dispatched. Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx> --- Changes in v2: - instead of extend thorlt_slice, extend wait time; block/blk-throttle.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/block/blk-throttle.c b/block/blk-throttle.c index c1bf73f8c75d..dc6140fa3de0 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -704,6 +704,9 @@ static unsigned long tg_within_iops_limit(struct throtl_grp *tg, struct bio *bio /* Calc approx time to dispatch */ jiffy_wait = jiffy_elapsed_rnd - jiffy_elapsed; + + /* make sure at least one io can be dispatched after waiting */ + jiffy_wait = max(jiffy_wait, HZ / iops_limit + 1); return jiffy_wait; } -- 2.39.2
